1 / 16

VOLCANOES

VOLCANOES. TYPES OF VOLCANOES. Volcanoes are classified by appearance Steep slopes = Strato/composite Volcanoes Gentle slopes = Shield volcano. Appearance predicts type of eruption Steep slopes → explosive (violent) eruptions Gentle slopes → non-violent (quiet) eruptions.

annona
Download Presentation

VOLCANOES

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. VOLCANOES

  2. TYPES OF VOLCANOES Volcanoes are classified by appearance • Steep slopes = Strato/composite Volcanoes • Gentle slopes = Shield volcano Appearance predicts type of eruption • Steep slopes → explosive (violent) eruptions • Gentle slopes → non-violent (quiet) eruptions

  3. TYPES OF ERUPTIONS ERUPTIONS FALL INTO 2 CATEGORIES Non-Violent (calm or quiet) eruptions build up the volcano Violent(explosive) eruptions destroy the volcano

  4. Strato/Composite Volcanoes Steep slopes – Explosive • Formed from viscous (thick) lava • Found in subduction zones & some hot spots Ex/: Casades, Mt St Helens, 2, 3

  5. Shield volcano Gentle slopes- Non-violent • Formed from fluid (thin) lava • Only found over a hot spots Ex: Hawaiian islands

  6. MAGMA/LAVA →ERUPTIONS Non-Explosive Eruptions: Fluid lava flows easilyallows gases to bubble away Explosive Eruptions: Viscous lava traps the gases until large pressures build up & the system explodes Pyroclastic flow (ash, rock fragments) flow out of vent

  7. ERUPTION HAZARDS LAHAR Water, mud & ash that flow like a river

  8. EXPLOSIVE HAZARDS PYROCLASTIC FLOW Travels over 200 mph Tephra = all ash & rock fragments • ash: pieces smaller than 2 mm; travel farthest • lapelli: small pieces between 2-66 mm • volcanic bomb: pieces larger than 64 mm Burns EVERYTHING in its path

  9. EXPLOSIVE HAZARDS VISCOUS LAVA (High Viscosity) • Cool temperature • Compositon: silica-rich (granitic) • Thick & gooey→Erupt violently; scattering ash and fragments widely • Does not flow very far;builds steep-sides; often destroys volcanoes Ex. rhyolithic & andesitic lava→ strato volcanoes

  10. NON-EXPLOSIVE HAZARD FLUID LAVA (Low viscosity) Higher temperatures Composition: Low silica (basaltic) Thin → Erupt “quietly” Great flows of lava that build mountains Ex. Basaltic lava→ shield volcanoes

  11. VISCOSITY→MAGMA/LAVA • Viscosity is resistance to flow • Viscosity determined by • Temperature HOT= thin, flows easily COOL= thick • CompositionSilica(SiO2)=mineral in magmaLOW SILICA (basalt) = thinHIGH SILICA (granite) = thicklow gas = flows easily

  12. WHAT KIND OF LAVA FLOW? • Fluid lava • thin ; flows far; • allows gas to escape; • quiet(non-violent) eruptions • builds mountain • Low Viscosity lava • Flows great distances Viscous lava • thick (granitic – high silica content) • traps gas • violent eruptions • destroys mountains

  13. FORMATION →ERUPTIONS Volcanoes are formed by • SUBDUCTION explosive eruptions • Sea Floor Spreading quiet eruptions • Hot Spotsusually quiet eruptions

  14. VOLCANO FORMATION: HOT SPOTS • A fixed source of magma rising beneath a plate forming volcanic islands • Magma can be basaltic or granitic –so eruptions can be explosive or “quiet”

  15. PREDICTING ERUPTIONS: VOLCANO MONITORING • Predict Eruptions by • Study and comparison of past eruptions • Warning Signs- • Small quakes (seismicity) • Swelling of slopes • Changes in water pH • Changes in gases emitted

  16. VOLCANO SUMMARY APPEARANCE → ERUPTIONS • Steep slopes (Strato volcano) → explosive (violent) • Gentle slopes (Shield volcano)→ non-explosive (quiet) MAGMA VISCOSITY → ERUPTIONS • Viscous (thick) magma → explosive (violent - Strato) • Fluid (thin) magma → non-explosive (quiet - Shield) FORMATION →MAGMA/LAVA →ERUPTIONS • Subduction zones → explosive (violent - Strato) • Sea Floor spreading zones → non-explosive (quiet- shield) • Hot spot → usually non-explosive, but can be explosive MONITORING→PREDICTION OF ERUPTIONS • Slope changes, quakes↑, water pH↓ , gases↑

More Related